The field of this invention has two aspects. The first aspect relates to a filament coating process to coat polyester filaments so as to protect the warp yarn from abrasive forces during weaving by means of a warp size. The second aspect relates to a fabric coating process, which is a modification of the filament coating process, to modify the surface properties of polyester fibers and fabrics so as to improve their hydrophilic characteristics with consequent improvement in antisoiling and antistatic properties under standard laundering conditions.
The general object of this invention is to provide a simple process of warp sizing 100% polyester filament. Another object is to provide a simple process of treating 100% polyester fibers and fabrics so as to improve the hydrophilic properties of these fibers. Another object is to obtain these improved properties with minimum modification of the hand of the material. Another object is to provide a process which utilizes the treating additive at a low level of application, thus obtaining an economic, efficient rate of use of the treating additive. Other objects appear hereinafter.
In the first aspect of this invention, in the production of woven fabrics, it is usually necessary to apply a suitable material to the warp yarns so that they may be adequately protected during weaving. The process by which the protective material is applied to the warp yarns is known as warp sizing. The function of the warp size is to protect the warp yarn from the tremendous forces of abrasion encountered during weaving. The warp size is required to be a readily-removable, film-forming adhesive polymer.
The adhesive film-forming materials used as sizing materials are usually polymers which are either water-soluble or may be easily solubilized with a mild alkali. The traditional size for warp sizes have been polysaccharides such as starches, proteins such as gelatin and casein, and vinyl polymers such as polyvinyl alcohol, polyacrylic acid and water-soluble acidic vinyl copolymers. However, materials of this type do not demonstrate the adhesion to 100% polyester filament necessary to provide the protection through the weaving process. The characteristics desired of a good warp size for 100% polyester filament are good abrasion resistance, good film flexibility, adhesion to the fiber, lack of sensitivity to atmospheric moisture and ease of removal. Therefore a need exists for a warp size composition which avoids the above disadvantage of adherence to 100% polyester filament.
I have now found that the process of coating 100% polyester filament with a low molecular weight high acid number polyester resin based on a dihydric alcohol having two to six carbon atoms and an acid having 3 to 5 carboxy groups protects the warp yarn from abrasive forces during weaving by functioning as a warp size. The preferred polyester of this invention is a trimellitic anhydride-neopentyl glycol polyester because of the absence of tack of this polyester.
The second aspect of this invention relates to the fact that many synthetic polymers such as polyesters, polyamides and polyolefins which are utilized as fibers suffer from the problem that they are relatively hydrophobic, that is, they lack an affinity for water and are relatively unable to either absorb or transport moisture along the surface of the fiber. This characteristic of hydrophobicity has been a persistent problem in the utilization of these synthetic fibers for garments. For example, a hydrophilic surface, i.e., a surface having a strong affinity for water, is particularly important in garments such as shirts and undergarments where rapid transmission of moisture is an asset. Hydrophobic fibers, if used for such garments, cause a cold, clammy feeling and a degree of discomfort to the wearer. Lack of moisture transmission also results in lack of breathing of the fabric which is attended by the wearer's tendency to assume the fabric is harsh and hard on the skin.
Hydrophobic properties of a fiber are also well-known as affecting its antistatic and antisoiling properties. Hydrophobic fibers when formed into shaped textile articles tend to accumulate static charges with a propensity to accept and retain grime and dirt. Synthetic hydrophobic fibers also tend to be oleophilic. Therefore, should oil and grime become embedded in the fiber, its hydrophobic properties tend to prevent water from entering the fiber to remove the contaminates therefrom. The difficult problem of cleaning oleophilic fibers makes desirable the modification of these properties to permit entrance of water for ease of cleaning.
A substantial amount of research has been performed in the textile industry to overcome the problem of the hydrophobic nature of these fibers by modifying their surface properties with a durable hydrophilic finish with attendant improvement in antistatic and antisoiling characteristics.
An example of a textile hydrophilic treatment process which functions by applying a polymeric coating is found in U.S. Pat. No. 3,236,685 to Caldwell et al. The polymeric coating adheres to the fiber by cross-linking a high molecular coating which provides a structured composition with an insoluble exterior that has the desired hydrophilic properties under conditions of wearing and laundering. The process described in this patent provides a hydrophilic insoluble coating having antistatic and antisoiling properties by coating the fabric with a solution or solutions containing a polyhydric alcohol and addition polymers of .alpha., .beta.-ethylenically-unsaturated acids. Under the proper conditions, the polyhydric alcohol reacts with the aliphatic polyacid to partially cross-link the polymer to provide an external coating of the fiber. The patentee states that ester linkages are formed to provide a partially cross-linked, flexible polymeric material which functions very much as an ion exchange resin. The polymeric polybasic acid is cross-linked to the extent that it is no longer soluble but some of the acidic ions are available to furnish ions for conducting static charges. The esterification is necessary to provide an insoluble coating with durability to standard laundering conditions. The patentee states the hand of the fabric is affected by the amount of the polymeric additive applied so a minimum amount consistent with effective surface characteristics is desirable.
Another example of a textile treatment process which improves the antistatic and water-absorption properties of the fiber is found in British Pat. Specification No. 1,358,195 to Brokmeier et al. This process modifies the polymer composition to attain the desired properties. Acrylonitrile polymer compositions are rendered antistatic and hydrophilic by the incorporation within the polymer composition of antistatic compounds which are miscible in polyacrylonitrile spinning solutions. This system imposes an added requirement on the spinning solution, that it be miscible with the antistatic compound. The additives are processed into the fibers and as much as 20% by weight of the polymer is additive.
The second aspect of this invented process therefore is to provide a new approach to this problem of modifying the hydrophobic properties of fibers to improve their hydrophilic, antistatic and antisoiling characteristics which permit the avoidance of the defects in the present methods used. As mentioned, the cross-linking polymeric approach can affect the hand of the material if more than minimum quantities are used. The incorporation of the surface modifying additive into the polymer through the spinning solution as in British Pat. Specification No. 1,358,195 requires that the additive be miscible with the spinning solution. The British Patent Specification states that quantities of additive up to 20% of the polymer weight are to be utilized, which represents a relatively large use of additive.
I have now found, in reference to the second aspect of this invented process, that the process of coating fabrics composed of 100% polyester filament fiber and yarn with a low molecular weight high acid number polyester resin based on a dihydric alcohol having two to six carbon atoms and an acid having 3 to 5 carboxy groups and curing said resin onto the polyester filament fiber and yarn improves the hydrophilic properties of these fibers. These esters cure onto the polyester fiber surfaces during a cure cycle to give a hydrophilic, antistatic, antisoiling textile finish. The modification of these surface properties occurs without excessive impairment of the critical properties of the coated fabric such as hand. The treating additive is applied at a low level, representing an economic, efficient rate of use. The preferred polyester of this invention is a trimellitic anhydride-propylene glycol polyester because of the durability of the hydrophilic finish.